Purines. Preparatory Study for the Syntheses of the Marine Sponge Purines Agelasimines-A and -B: Synthesis and Acetylation of Their N(7)-Benzyl Analogues

Abstract

Four-step synthetic routes from 3-methyladenine (10) to 7-benzyl-N6,3-dimethyladenine (lb) and 7-benzyl-l,2-dihydro-l,3-dimethyladenine (2b), selected as models for the marine sponge alkaloids agelasimine-A (la) and agelasimine-B (2a), respectively, have been established. The key steps involved are regioselective methylations of 7-benzyl-3-methyladenine (8) and 7-benzyl-1,2-dihydro-3-methyladenine (11). The reaction of lb with acetic anhydride in pyridine was found to give the monocyclic imidazole derivative 29b. A similar acetylation of 2b yielded the N6-acetyl derivative 20b. When treated with boiling H2O,20b afforded 7-benzyl-2,3-dimethylhypoxanthine (21b) and a compound inferred to be the dihydrohypoxanthine derivative 30. Probable pathways to 29b from lb and to 21b and 30 from 20b are proposed. © 1994, The Pharmaceutical Society of Japan. All rights reserved.